The load on the shaft is increased. The rotor slows down momentarily, as it required some time to take increased power from the line. In another word, it can be said that even if the rotor is rotating at synchronous speed, the rotor slips back in space because of the increase in the load.
What speed does a synchronous motor run at full load?
The synchronous speed is 1500 rpm and the typical full load speed is 1450 rpm. The slip is the difference between synchronous and load speed – 50 rpm.
What happens to the V curve when a synchronous motor is loaded?
V curve is a plot of the stator current versus field current for different constant loads. If now, the field current is increased further, the armature current increases and the motor starts operating as a leading power factor. …
How does synchronous motor change speed?
Changing the number of poles is not easy, so we do not use that method. However, with the invention of solid-state devices, the frequency of the current fed to the synchronous motor can be varied. We can control the speed of the synchronous motor by changing the frequency of the supply to the motor.
What is the speed of synchronous motor?
The synchronous speed of an AC motor is determined by the frequency of the source and the number of poles. The RPM is calculated by multiplying the frequency times 60 and dividing by the number of pairs of poles.
What is the effect of load on synchronous motor?
The load on the shaft is increased. The rotor slows down momentarily, as it required some time to take increased power from the line.
What is the main disadvantage of synchronous motors?
Disadvantages or Demerits:
Synchronous motors requires dc excitation which must be supplied from external sources. Synchronous motors are inherently not self starting motors and needs some arrangement for its starting and synchronizing. The cost per kW output is generally higher than that of induction motors.
Why the speed of synchronous motor is constant?
The rotor of a synchronous motor moves at the same speed as the changing, rotating field in its stator. The rotor’s magnetic field is “synchronized” with the stator’s field. … Their speed is dependent on the number of poles and the supply frequency. They have a constant speed at a given supply frequency.
Does the excitation affect the synchronous motor speed?
why speed decreases as field excitation increases in synchronous machine. why the speed of the synchronous motor remains constant on any load. why with the change of excitation of a synchronous motor the magnitude of armature current first decrease and then increase.
What happens when motor load increases?
As the load is increased, the motor will slow down, and the torque will increase. Current into the motor will also increase. If the load is increased above the maximum, the motor may overheat after a while. … The peak torque occurs at relatively high speed for efficient motors.
What is the difference between synchronous speed and rotor speed?
Induction motor with squirrel cage rotor has two different speeds. The synchronous speed refers to the stator rotating magnetic field, which depends on the number of poles and frequency. The other speed is the rotor’s. The rotor speed will be always slower than the stator speed, we call it slip.
How do you control the speed of a synchronous motor?
Speed of synchronous motors can be controlled using two methods called open loop and close loop control. Open loop contol is the simplest scalar control method where motor speed is controlled by independent frequency control of the converter.
What is true synchronous mode?
In true synchronous mode, the stator supply frequency is controlled from an independent oscillator. Frequency from its initial to the desired value is changed gradually so that the difference between synchronous speed and rotor speed is always small. This allows rotor speed to track the changes in synchronous speed.
What is synchronous speed?
: a definite speed for an alternating-current machine that is dependent on the frequency of the supply circuit because the rotating member passes one pair of poles for each alternation of the alternating current.
What is asynchronous speed?
Synchronous motor is a machine whose rotor speed and the speed of the stator magnetic field is equal. Asynchronous motor is a machine whose rotor rotates at the speed less than the synchronous speed.
What is slip speed?
The speed at which the induction motor work is known as the slip speed. … The difference between the synchronous speed and the actual speed of the rotor is known as the slip speed. In other words, the slip speed shows the relative speed of the rotor concerning the speed of the field.